ASTM A904-20

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Designation: A904 − 14 A904 − 20
Standard Specification for
50 Nickel-50 Iron Powder Metallurgy Soft Magnetic Parts
This standard is issued under the fixed designation A904; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This specification covers the magnetic properties of 50 nickel-50 iron parts fabricated by powder metallurgy techniques and
is intended for parts that require high magnetic permeability, high electrical resistivity, low coercive field strength, and low
hysteresis loss. It differs from the wrought alloy specification (see Specification A753) because these parts are porous. A number
of magnetic properties such as permeability are proportional to the sintered density.
1.2 This specification deals with powder metallurgy parts in the sintered or annealed condition. Should the sintered parts be
subjected to any secondary operation that causes mechanical strain, such as machining or sizing, they should be resintered or
annealed.
1.3 The values stated in customary (cgs-emu and inch-pound) SI units are to be regarded separately as standard. The values
given in parentheses are mathematical conversions to SI customary (cgs-emu and inch-pound) units, which are provided for
information only and are not considered standard.
1.3.1 There are selected values presented in two units, both of which are in acceptable SI units. These are differentiated by the
word “or,” as in “μΩ-cm, or, Ω-m.”
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
A34/A34M Practice for Sampling and Procurement Testing of Magnetic Materials
A340 Terminology of Symbols and Definitions Relating to Magnetic Testing
A596/A596M Test Method for Direct-Current Magnetic Properties of Materials Using the Ballistic Method and Ring Specimens
A753 Specification for Wrought Nickel-Iron Soft Magnetic Alloys (UNS K94490, K94840, N14076, N14080)
A773/A773M Test Method for Direct Current Magnetic Properties of Low Coercivity Magnetic Materials Using Hysteresig-
raphs
B328 Test Method for Density, Oil Content, and Interconnected Porosity of Sintered Metal Structural Parts and Oil-Impregnated
Bearings (Withdrawn 2009)
B962 Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle
E1019 Test Methods for Determination of Carbon, Sulfur, Nitrogen, and Oxygen in Steel, Iron, Nickel, and Cobalt Alloys by
Various Combustion and Inert Gas Fusion Techniques
3. Terminology
3.1 The terms and symbols used in this specification are defined in Terminology A340.
This specification is under the jurisdiction of ASTM Committee A06 on Magnetic Properties and is the direct responsibility of Subcommittee A06.02 on Material
Specifications.
Current edition approved May 1, 2014June 1, 2020. Published May 2014July 2020. Originally approved in 1990. Last previous edition approved in 20092014 as
A904A904 – 14.–09. DOI: 10.1520/A0904-14.10.1520/A0904-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A904 − 20
4. Ordering Information
4.1 Orders for parts conforming to this specification shall include the following information.
4.1.1 Reference to this standard and year of issue/revision.
4.1.2 Reference to an applicable part drawing.
4.1.3 Quantity required.
4.1.4 A critical cross section of the part shall be defined and so indicated on the applicable part drawing. The location of the
critical section is by mutual agreement between the user and producer (see 6.2).
4.1.5 Magnetic property requirements if they are other than stated in 7.5.
4.1.6 Certification of chemical composition or magnetic property evaluation, or both (Sections 5 and 7).
4.1.7 Marking and packaging requirements (Section 12).
4.1.8 Exceptions to this specification or special requirements such as functional testing as mutually agreed upon by the producer
and user.
5. Chemical Composition
5.1 The chemical composition of the parts shall conform to the requirements prescribed in Table 1.
5.2 Determination of metallic constituents shall be by a method acceptable to both producer and user. Analysis of carbon,
nitrogen, sulfur, and oxygen shall be done in accordance with Test Methods E1019.
6. Sintered Density Requirements
6.1 Magnetic and residual induction properties of powder metallurgy parts strongly depend on density. The density of powder
metallurgy parts is determined by the compressibility of the powder, the compacting pressure, and sintering practice (temperature,
time, and atmosphere).
6.2 Parts produced in conformance with this specification shall have a minimum sintered density of 6.99 g/cm6990 kg
3 3
(6990 kg ⁄m ) , or, 6.99 g/cm in the critical section of the part. The critical section shall be defined by agreement between the user
and producer.
6.3 Sintered density shall be determined in accordance with Test Method B328 (which has been replaced by Test Methods
B962).
7. Magnetic Property Requirements
7.1 Because of the nature of powder metallurgy parts production, magnetic testing of each lot is not required by this
specification. Nevertheless, it is strongly recommended that the user require the producer to conduct periodic magnetic evaluations
and to certify such results. Such magnetic property evaluations shall be conducted in the manner described below.
7.2 When requested, each lot of parts should be sintered with at least one and pre
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